Objective       To investigate the anatomy features of minimally invasive surgical trajectory to expose ventral brain stem in transpetrosal-presigmoidal approach based on virtual reality image model.       Methods       CT and MRI scanning was performed to 15 adult cadaver heads

and then the obtained image data were inputted into Vitrea virtual reality system to establish 3-D anatomy model of jugular foramen region. Transpetrosal-presigmoidal approach exposing ventral brain stem was simulated by selecting osseous and root entry zoon of cranial nerve as landmark points to draw a cylinder. Anatomic exposures in surgical trajectory following alternation of different minimally invasive approaches were observed

measured and compared.       Results       Spatial sequence of nerves and vessels in the route simulating transpetrosal-presigmoidal approach to expose ventral brain stem was displayed clearly. The volume measuring for petrous bone in 3-D image model showed: route b route c route a

and that for lower cranial nerves showed: route c route b route a. The volumes of veins and anterior inferior cerebellar artery were largest in the route a

that of facial-acoustic nerve complex in the route b was larger than that in route a

and that of vertical segment of facial nerve in the route c was larger than that in route a (all P0.05). No significant difference was seen in  the volume of labyrinth between the route b and c (P0.05).       Conclusion       Virtual reality system is of great help to understand the spatial architecture relationship among osseous structures

nerves and vessels involved in presigmoidal approach to expose different targets of ventral brainstem.